In typical conventional radial compressor impellers, especially of the so-called dual flow type wherein integrally formed radial impeller blades are arranged back-to-back, or on two sides of one impeller component, it is practically impossible to compensate or balance impeller imbalances by means of local removal or addition of material in a manner avoiding any aerodynamic impairment of the blade profiles and canal structures, which have been precisely produced according to stringent production criteria.
In such a rotor concept the dual flow or double suction radial impeller is welded together or formed as one integral unit including front and rear shaft stubs in order to satisfy the necessary stiffness and the strength requirements despite the sharply tapered or narrow contour of the rotor components sloping inwardly toward the rotor axis. The radially relatively narrow portions of the circumferential rotor contour in conjunction with a relatively long component length, have their cause among others in that relatively high mass throughputs and high inflow velocities into the dual flow radial impeller must be satisfied by the compressor even if the compressor has relatively small given local rotor diameters. Due to the just described construction balancing, even by so-called balancing collars, cannot be realized. Such a so-called balancing collar is a circumferential material web which may be machined away from the inside to compensate imbalances, whereby the collar would be located in the material of the dual flow impeller on the front side or back side thereof, if there were space. Thus, at best, such collars could perhaps be realized as attachment impellers, removably seated on the shaft. However, such balance impellers would require relatively large rotor diameters and they would have to be placed on both sides of the dual flow compressor impeller. Besides, a removable attachment impeller is often not desirable, because it weakens the rotor. However, in such a concept a balancing collar type circumferential flange or the like could be covered by a respective attachment impeller in a flow dynamically smooth manner. Only dynamic local imbalances could be corrected in such a described rotor having a dual flow compressor impeller with integrally formed or attached shaft stubs, in that a local material removal or machining is carried out at the respective bearing area on the shaft stubs. However, such a material removal cannot influence or correct any static imbalances of the dual flow impeller which has the largest rotor mass.